The present invention relates to an axle unit for a vehicle such as an automotive vehicle and particularly an axle unit provided with a rotational speed sensor for detecting a rotational speed of a vehicle wheel.
An example of such an axle unit is disclosed in Japanese Patent Provisional Publication No. 2000-249138.
In the axle unit, an encoder in the form of a circular ring or disc for detecting rotation of a vehicle wheel is attached to an end of an inner wheel (axle) that rotates together with the vehicle wheel. On the other hand, on the outer wheel (hub bearing) side is disposed a sensor for detecting rotation of the encoder and therefore rotation of the vehicle wheel in such a manner that a detecting section of the sensor is positioned opposite to the encoder. Further, the end portion of the inner wheel that is located on the side where the encoder is provided is closed by a cover made of a non-magnetic material so that the encoder and the detecting section of the sensor are position opposite to each other with the cover being interposed therebetween.
By so constructing the axle unit, water, chips of iron, etc. never intrude into the space between the sensor and the encoder, thus making it possible to prevent the sensor and the encoder from being damaged due to freezing while preventing a disorder in the regular and periodic variation of the magnetic characteristics of the encoder and deterioration of the same.